Phase-sequence wattmeter system



Dec. 12, 1933. R, EVANS 1,939,044

PHASE SEQUENCE WATTMETER SYSTEM Filed July 3, 1931 Fig.1.

ll/ w :2 X w Dc v v VN WITNESSES. INVENTOR Robe/f D. Evans BY PatentedDec. 12, 1933 UNITED STATES.

. 1,939,044 mass-snowmen WATTMETER' Y SYSTEM I Robert D. Evans,Swissvale, Pa., assignor to Westinghouse Electric & ManufacturingCompany, a corporation of Pennsylvania Application July 3,1931. SerialNo. 548,592

Claims. (Cl. 172-245) -My invention relates to phase-sequence wattmetersystems and it has particular relation to a wattmeter system formeasuring the total watts, either real or reactive,,in a four-wire,three-phase 5 system having (preferably nearly balanced) lineto-neutral,single-phase loads, say at 120 volts, and balanced polyphase apparatusconnected across the three delta-phaseterminals of, say, 208 volts.

In such four-wire systems, the accurate determination of the total powerutilized has heretofore been quite difficult, requiring a plurality ofwattmeters, on account of the slightly unbalanced load conditions.Expressing the real and reactive powers P and Q in phase-sequencequantitles, in accordance with the system of symmetrical coordinateswhich is now the accepted method of solving unbalancedpolyphaseprobilems, we have Y P+JQ=P1+P2+Po+i(Q1+Q2+Qo) where thesubscripts 1, 2 and 0 refer to the positive, negative and zerosequencecomponents respectively. The-real power may also be written effect of mymeteringsystem is to slightly penalize such a customer, increasing his,bill by; an amount corresponding to, the increased losses due tozero-sequence currents :in the powersystem, as pointed out in a paper by'Dr. Fortescue in American Institute of Electrical EngineersTransactions, vol. i=2,v 1923, page 363. a

By makingno attempt to meter this zero-sequence power component, Ihavebeen able to produce a metering system utilizing only two meterelements, which may easily be mounted to operate on the same disc,sothat a single meter, of substantially standard size and construction,

first twocurrent transformers being in t'woof may be utilized forsecuring a substantially accurate measure of the real or reactive powersP or Q, according to the connections. 1 1

In all such metering systems, one of the important considerations, whichis insisted upon by most customers today, is that the metering systemshall besimple,and easily checked as toaccuracy, without depending uponcomplicated networks and calculations for arriving at a determination ofits accuracy. The metering system which I have evolved fully meets.these require- 06 ments.

' In thedrawing," p

. Figure v1 is a diagrammatic view of circuits and apparatus embodyingmy invention in apreferred form,

Fig. 2 is a partial view showing how the.con-' nections would be changedto measure reactive power instead of real power, and I 1 Fig. 3 is aview similar to Fig. 1, showingan equivalent circuit. u g

In Fig. 1, the four-wire, three-phase system is shown at a, b, c, N,where a, b, c are the threephase conductors and: N is the neutralconductor. The meter consists of two wattmeter elements W and W, whichmay be either two complete wattmeters or simply two wattmeter fieldelements operating on a single disc (not shown).v The essential factthat the two'wattmeter elements exert torque on the same shaft isindicated in thedrawing by showing a single wattmeter shaft 3.

The wattmeter element W has a voltage wind ing 4 and a current winding5. In like manner, the. other wattmeter element W hasa voltage winding 6and a current winding 7. The two voltage windings 4 and 6 are energizedfrom a potential transformer bank so that the voltage winding 4. isimpressed with a voltage (El.7b),-whereas the voltage winding 6 isimpressed with a voltage (EcEb) where Ea, Eb and E0, in'this case,represent the star voltages of the system. I

-' The currentcoils 5 and '7 are energized from fourcurrent'transformers8, 9, 10 and 11, the

the phase conductors, such as a and c, respective- 9 ly, and the lasttwo current transformers beingin the neutral N, or these twocurrenttransformers may be combined into a. single transformer havingtwo secondary windings. Theratios' of the numbers of turns of theprimary and secondary windings of the current transformers are such thatthe transformers in the neutral conductor N'respond to one-third oi thevalueof the current in the neutral conductor, whereas the u transformersin the phase-conductors a and c W is energized in response to (fa-iN/3)whereas the current winding 7 of the otherwattmeter element W isenergized in accordance with (LAW/3). U

The watts or torque measured or produced in or by the two wattmeterelements W and W may e be indicated by the symbols W and We, as follows.

These equations hold true for star voltages and utilizing the well-knownsymbol Otto indicateone of the cube roots of unity, so that oc+cc +l=0ZY ee le t r a v A A V v I e V E I (1-a)+E2 2( w =+it ahl doi w Iw+w'=sat+s it. n will be observed that each wattmeter el develops atorque proportional to the product of the voltage and current which aresupplied to its respective voltage and current windings; It mu mrther benoted that'one wattmtlter develops a. torque which is responsive to thealgebraic sum of a certain coefficient at times the positive-sequencewatts iii i1 and another coefficient in times thenegative-sequenceiwatts E2 is plus an unwanted quantity or quantitiesincluding the productor products of a voltage component or components ofone phasesequence'times a current component. or components of anotherphase-se quence. The other wattmeter element develops a'torque which isresponsive to the algebraic sum of 1; times the positive-sequence wattsplus (i times the' negative-sequence watts minus the same unwantedquantity or quantities; so that the total response is equal to (4+5times the sum or the positive and negative-sequence watts. In theparticular case shown in the drawing,

' If it is desired to have a composite wattmeter respond to reactivewatts instead of real watts,

the voltagewindings 4 and 6, instead of being connected in series withan'external resistor 12,

p as in Fig. 1, which is the usual wattmeter 00111160.-

. (Eai.b) equals the delta voltage he, indicated 751 tion; may beconnected in series with an external j inductorlii, as indicated in-Fig.2, which causesthe currenttraversing the voltage coil to lagsubstantially behind the applied voltage. The lag of the currents in-thevoltage "coils of the" wattmeter elements maybe 'made exactly '90?- bymeans of a suitable shunt 15 connected across .each voltage ;coil, asindicatedin Fig. 2, said shunt-being either a high resistance or a highcapacitance, preferably the former. V v Since the difference of the twostar voltages y icapital subscript',and since'(Ebfi1,c)=EA;

delta currents as well as for delta voltages and star currents. Thus, wemay make )f =(E W) f -h Figt shows axtwo -element wattmeter inaccordance withthese equations. One wattmeter element W: has a voltagecoil 4; responding to /3 EC-EB)'= /3(Eu 1by- V I Z I Ea-Ea)=ua--Eo and acurrent coil 5' responding to (his) which equals Io." The otherwattmeter-element W11 has a voltage coil 6' respondingto V g r wri e'%(E'o-Ec) wit-1ft) l (EcEc) and a currentcoil Ti responding to iit ie)which equals Li. 7

*Inthe metering devices of Fig. 3,one meterelement W1 respondsproportionately to thevertorial product'ol a star voltage its and thenext leading delta current is, in the delta phase which leads the lineto-neutralvoltage is by 30 at unity power factor,- there being noherosequencecomponent in either factor of the prodnot; while the othermeter-element Wn responds in the opposite direction proportionately tothe vectorial productof the star voltage file, which leads the voltageis by 120,when the loads are 7 balanced, and the next leading deltacurrent is,

in the delta phase which leads the 1ine-to-neutral voltage file by '30"at unity power'factor, there being no ZEIO SBQUEHCGCOmPOIIGHt in eitherfac torof the product. f As before stated,v the voltage and currentsymbols'may be interchanged.

Whenever, in the foregoing specification, or in the appended claims, Irefer to a meter; or wattmetr, I mean'to include either an indicat-"ing, integrating; recording or contact-making instrument or el y.responsive to the quantities indicated. 7' e V It will be obvious thatmany changes and medi ncations may be made, within the spirit of myinvention, and'I do not desire that the appended claims shall'belimited'by the specific constructions'illustratedin the drawing, exceptas may be required by' thelanguage of the claims, when read inthe lightof the prior art. 1

I claim as my-inventionz ,mately balanced single-phase line-to-neutralloads. and three-phase loads, said metering-age gregate comprising twowattmeter elements ex- 'e'rting torque on the same shaft, each wattmeterelement having a 'currentwinding' and a 'voltage winding, and means forso energizing the several voltage and current windings of the twowattmeter elements that one element responds'to the algebraic sumof dtimes the positive-sequence watts plus h times the negativesequencewatts plus an unwantedquantity or quantities including the product orproducts of a -voltage component -or-componentst :of one phase-sequencetimes a current component or components of yanotherphase sequence, 6 andb being any coefficients, while the other element responds to thealgebraic sum of b times the positive-sequence wattsjplusd times "thenegative-sequence watts minus the same unwanted quantity'or quantities.

2. A metering-aggregatefor measuring the total amount of power on afour-wire, three-phase, power-distribution line having approximatelybalanced single-phase line-to-neutral loads and three-phase loads, saidmetering-aggregate comprising two wattmeter' elements exerting torque onthe-same shaft, each wattmeter element having a current winding and avoltage winding, and means for so energizing'the several voltage andcurrent windings of the two wattmeterelements that one element respondsto the algebraic sum of a times the positive-phase sequence' watts plusbtimes the negative-phase-sequence watts plus an unwanted quantity orquantities including the product or products ofa voltage component orcomponents of one phase-sequence times a current component or componentsof another phase-sequence, ji and}; being anymoefllcients, while theother element responds to the algebraic sum of 2; times thepositive-phase-sequence watts plus 'd times the negative-phase sequencewatts minus the same unwanted 'quana tity or quantities, where d 1.-tand 12:1 -11, whereas a is one of the cube roots of unity'.

3. .A metering-aggregate for measuring the total amount of power on afour-wire, three-phase, power-distribution line having approximatelybalanced single-phase line-to-neutral loads and three-phase loads, saidmetering-aggregate comprising two wattmeter elements exerting torque onthe same shaft, each wattmeter element having a current winding and avoltage winding, and meansfor energizing the several voltage and currentwindings of the two wattmeter elements, the first wattmeter elementbeing designed and connected to respond to any function of voltage andcurrent which includes two components, one component being any functionof the power which is to be measured by the metering-aggregate as awhole, and the other component being any other function of the currentand voltage, the second wattmeter element being designed and connectedto respond to any functionof voltage and current which includes twocomponents,

vone component being any function of the power which is to be measuredby the metering-aggregate as a whole, and the other component being thesame other function to which the first wattmeter element responds, butopposite in the direction of response.

f 4. A metering-aggregate. for measuring the sum ofzthe positive andnegative-sequence power on a fourwirepthree-phase, power-distributionline having single-phase lineeto-neutral loads and three-phase loads,said metering-aggregate comprising two wattmeter. elements exertingtorque on the same shaft, each wattmeter element having a'currentrwinding and a voltage" winding, so that each wattmeter elementre'-' sponds' to the; vectorial; productpf the current andvoltageapplied to its windings, and means for energizingone of saidwattmeter elements to respond to the vectorial productof (lifa-1hb) and(Na-NW3), and means for energizing the other -of said wattmeterelements, to respond to the vectorial product of (Me-Mb) 4 and(Nc',Nzv/3), wherethe symbol M represents one of the pair comprisingcurrents and voltages, measured in one of theways comprising delta andstaiyand the symbol jN represents the other of the pair comprisingvoltages and currents, respectively, measured in one of the wayscomprising delta and star, andthe subscripts a, b, c and N referrespectively to the three phases and the neutral phase or three timesthe zerosequence phase component. I

5. A metering-aggregate for measuring the sum of thepositive-andnegative-sequence power on a four-wire, three-phase, power-distributionline having single-phase line-to-neutral loads' and three-phase loads,said metering-aggregrate comprising' two wattmeter elements exertingtorque on the same-shaft, each wattmeter element having a currentwinding and a voltage winding, so that each wattmeter elementresponds'to the vectorial product ofthe current and voltage'applied toits windings-,andmeans for-energizing one of'said wattmeter elements torespond to the vectorlal product of (filleibland (ia I N'/3),"a'nd meansfor energizing the other of said-wattmeter ele-' mentsto respond to thevectorial product of (Ec-Eb) and (I'i1v/3), the symbols Ea, Eb and ECrepresenting star voltages in the respective phases a, b and c, and thesymbols ia, 1c and in representing the currents in the phase conductorsa and. c'and in the neutral,

6. A metering-aggregate for measuring the total amount of reactive poweron a four-wire,

three-phase, power-distribution line having smgle-phase line-to-neutralloads and three-phase loads, said metering-aggregate comprising twowattmeter elements exerting torque on the same shaft, each wattmeterelement having a current winding and a voltage winding, and means for soenergizing the several voltage and current windings of the two wattmeterelements that one element responds to the algebraic sum of 5.

'7. A metering-aggregate for measuring the sum of the positive andnegative-sequence reactive power on a four-wire, three-phase,powerdistribution line having single-phase line-td-n'eutrel loads andthree-phase loads, said meteringaggregate' comprising two wattmeterelements exerting torque on the same shaft, each wattmeter elementhaving a current winding and a voltage winding, so thateach wattmeterelement responds to the vectorial product or thecurrent and'voltageapplied to its wmdings,-and.means for energizing one 01!. said wattmeterelements to respond to the vectorial product of 1 (Er-Eb) and It m/3),and means for energizing the other of said wattmeter elements to'respondto the vectrial productof i (Ed-Eb) and (It-4M3), the symbols in, in andis representing star voltages in the respective phases a, b and 'c, andthe symbols 11', lo and in representing the currents in the phaseconductors a and c and in theneutral. m V

8. A metering-aggregate for a four-wire threephase system havingline-to-neutral single-phase loads and polyphase loads, comprisingtwowattmeter-elements responding to the products of the vectorialquantities MC-(Na-NO)- and -MMNw-Nri), wherethe symbol M representseither a voltage-vector or a conjugate currentvector, while Nrepresentseither a conjugate curwith the quantity Mo, means forenergizing the other windingmeans of the first wattmeter-element inaccordance with the quantityiNa No) means for energizing oneof thewinding means of the second wattmeter-elementin accordance with thequantity MA, and means for energizing the other winding means of thesecond wattmeter-element in accordance with the quantity (Nc No),whereby the responses to Mo(N-No), and -MA(Nc-N) are obtained.

9. A metering-aggregate fora four-wire threephase system havingline-to-neutral single-phase loads and polyphase loads, comprising twowattmeter elements responding to KEd-EB) To and /;(l54-Es) 14,respectively, the symbols in, EB

in accordance with some function of (EA-is),

and means for energizing the. current-responsive winding means of thesecond wattmeter. element in accordance with-'some iunctionof in,whereby the responses to V (Ec-:Es)fc end1 (E.4+,-En)h areobtained. V

10. A metering-aggregate for a four-wire threephase system havingline-to-neutral single-phase loads and polyphase loads, comprising twowattmeter elements, each wattmeter element compris- 1 ing two windingmeans so related as to develop a torque responsive to a function of theproduct v of respectiveenergizations of said two winding means, meansfor energizingone of the winding means ofithe first wattmeter elementproportionately to a star current or voltage, respectively, with nozero-phase-sequence componentin said proportionality, meansiorenergizing the, other windingv means of the first wattmeterelementproportionately to thenext leading delta voltage or current,respectively, with no zero-phase-sequence component in saidproportionality, means for energizingoneof the windingmeans of thesecond wattmeter element proportionately to the star current or voltagewhich leads the firstmentioned star current or voltage, respectively,with no zero-phase-sequence componentin said proportionality, and meansfor energizing the other winding means of the second wattmeter ele mentproportionately? to the next leading delta voltage orcurrent,'respect1vely, with no zeros phase-sequence component in saidDI'ODOItlOIb,

ality, the direction of response of the second wattmeter element beingopposite to that of the first. M f' c ROBERT D. EVANS.

